Conventionally, in a driving tool such as a pin tacker, which is used mainly for connecting woods or plaster boards, a biasing force of a compression spring or pneumatic cylinder has been used as a driving force. In the former case, an electric motor has been used as the driving source by which a driver (for striking a nail etc.) is retracted to its stand-by position against a spring force (driving force for striking the nail). In this description, driving tools in the former case may be called electric driving tools, whereas driving tools in the latter case may be called pneumatic driving tools.
U.S. Pat. No. 7,513,407 discloses a prior art relating to the electric driving tools. In more detail, the patent document discloses that a rack and pinion mechanism is arranged between a driver for striking a driven member such as a nail, and a weight device for reducing a counterforce, and the weight device is moved in a direction opposite to a driving direction of the driver in order to reduce the counterforce.
According to the counterforce-reducing mechanism of the above prior art, the movement of the driver is synchronized with that of the weight device. However, it is difficult to stop the driver and the weight device simultaneously. That is, in a case where after one of the driver and the weight device stops moving, the other continues to move slightly according to its inertial force. Consequently, a large impact is applied to engaging teeth of the rack and pinion gear, which deteriorates durability of the rack and pinion mechanism. This is especially so, since in the prior art disclosed in the above patent document, no damper is disposed for the driver. Thus, because of this mode of construction, after the weight device is stopped, the driver still moves due to the inertial force, and thus a large undesirable impact is applied to the engaging teeth of the rack and pinion mechanism.
Thus, there is a need in the art to provide a mechanism for reducing an impact by the counterforce applied to the driving tool when the driven member is driven by the driving force, where such a reduction would substantially improving the durability of the rack and pinion mechanism.